1. Field of the Invention
The present invention relates generally to a method for increasing pattern density, and more particularly to a method of using a single photo mask and a single shot to form a dense pattern.
2. Description of the Prior Art
Many factors, including demand for increased portability, computing power, memory capacity and energy efficiency, have led to integrated circuits being continuously reduced in size.
This means that density of semiconductor elements on a wafer has increased with the advancements in the semiconductor industry. In particular, miniaturization of microelectronic elements has made the intervals between elements shorter and shorter, which increases the difficulty of a lithographic process.
The lithographic process is commonly used to pattern features. Due to factors such as optics and the wavelength of light used to pattern the features, lithographic techniques have a resolution limitation.
For current lithographic tools, it is impossible to create semiconductor elements with pitch lower than the resolution limitation in one exposure. The current solution is that the desired semiconductor elements are patterned by two exposures using two photo masks, respectively, on a photo resist layer. This process is then followed by one etching step. The current method incurs a high processing cost, however.